Huygens Institute - Royal Netherlands Academy of Arts and Sciences (KNAW)

Citation:

A.F. Holleman, The preparation of and its chloride, in: KNAW, Proceedings, 7, 1904-1905, Amsterdam, 1905, pp. 189-191

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- 1 - ( 189 ) investigation, and of which the theol'y of VAN mm WAALS could give a closer description. The peculiarity of the examined system, which lies in the fact that the vapour pressure of the one substance (ether) far exceeds that of the othel' (anthraquinone), caused some wholly unexpeeted phenomena, and made it on the other hand possible to realize retro­ grade solidification on a much largeJ" seale than had been thought posóible till now. Laboratol'Y fOl' Anorglmic CAernistry of tlte UniV81'sity. Amste1'Cla1T/', June 1904.

Chemistry. - "Tlte lJ1'epamtion of silicon anc! its c/doricle." By Prof. A. F. HOI,LEMAN.

(Commumcated in the meeting of June 24, 1904).

The nmnerons proposals which have been made for tIle prepara­ Lion of the element silicon in both the amorphous and crystallised torm prove that a simple method has not as yet been found. W. HElIIPEL and VON HAASY 1) have published in 1899 an additional process consisting in the decomposition of silicon fluoride with . 'fhey melt this metal in small portions at a tIme in an iron apparatus and then pass over the mass a current of silicon fluoride, which is then very readily decomposed. The brown porous mass, whieh has been brought to a faint red heat is allowed to cool for two or three homs in the current of sihcon fluoride. An attempt to convert it into silicon chloride by heating the mass without previons purification in a CUl'rent of ehlorine was unsnccessful. It was nnpossible to remove the Na Fl and Na2 Si Flo by boiling with ; so in order to obtitin pure silicon it 'was lleCeSSal'y to fnse the mass with &odinm and aluminium. Thc latter dissolves tlle silicon which 1& thcn left lll,>olnble on tl'ealIllg Ilte regnlus with dilnte hydro­ chlol'ic acid. 1\11'. H. J. SUJPBR who has l'cpealec\ Ihese eÀpel'Îments in 111y laboratory sbowed (1) that by a small ll1odification of the process lbc el'ude product may be pllrified to sneh an eÀtent by boiling with water that it may be used for preparing silicon chloride; (2) tIle 1'eason why Ihe erude prodnrt on being treated with chlorine does not yield slltcon chloride.

1. 1t is known tbat &odil1l11 fluoride l'eadily absOl'bs SI F1 4 and

') ZeÎlschl·. f. anOl'g. eh. 23, 32. 13l1<

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passes into Na2 Si ~'16' By allowing their apparatus to cool for 2 to 3 hoUl's whilst transmitting this gas HEMPEL and VON HAASY practically converted the , which had been formed according to the equation: 4Na+SiFI4 =4NaFI+Si, intosodium fluosilicate, which is soluble in water with gl'eat difficulty. If, however the action of Si F1 4 is stopped as soon as all the sodium has been introduced into the apparatns, it is easy to almost completely avoid the formation of Na2 Si Fla. 100 grams of sodium yielded to Mr. SLIJPER 219 grams of crude material (4NaFl + Si) instead of213.6 the quantity calculated; 55 grams of the Na gave 119 grallls, theory 117.2, and in some further experiments the theoretical quanlity was but little exceeded. By washing and boiling with water and with dilute hydrochloric acid the 119 grams were reduced to 20 grams whilst the product may contain 16.7 grams of silicon. The product so obtained is not, however, pure amorphous silicon, only about 40 pE>r cent is volatilised in a current of chlorine and may be condensed as silicon chloride, and a residue is obtained, which is only to a slight extent soluble in water and principally consists of silicon dioxide. This must have been formed during the washing; for if the crude product is heated in a cm'rent of chlorine there remains besides only a very small quantity of insoluble residue. As the crude product when lmmersed in water causes a visible evolution of gas with the odoUl' of Si H4 it is probable that the Si O2 has been formed by decomposition of Si R4 which may have been pro­ duced by the action of water on some sodium silicide. MOISSAN has recently shown that on treating silicon with boiling water the dioxide of that element is formed. 2. In accordance with HEMPEL and VON HAASY, Mr. SLIJPER found that on heating the crude product in a current of chlorine not a trace of silicon chloride is oblained. Ab the said product consists mainly of 4 Na Fl + Si, it was surmised that this must be attributed to the fact that the primary formed silicon chloride reacts with sodium fluoride according to the eCluation

Si 01 4 + 4 Na FI = Si Fl4 + 4 Na Ol It appeared indeed that on heating sodium fluoride or sodium fluosilicate in the vapour of silicon chloride the said decomposition takes place. If, therefore, chlorine is passed over a mixture of Si and Na FI as is present in the crude product the reaction must proceed in this marmer:

Si + 4 Ol + 4 Na Fl = Si F1 4 + 4 Na Ol.

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That such is practically the case was shown by the fact that the gas evolved consisted of Si Fl4 and that the substance left behind in the boat was found to be almost pure sodium chloride. A better method of preparing amorphous silicon fleemed to be the decomposition of silicon chloride by sodium. When boiled in bel1zene-solution with sodium Ol' potassium no action took place. A reaction, however, took place on heating sodium in the vapour of silicon chloride, but it became very violent; the brown powder obt.ained could certainly be readily freed from sodium chloride by means of water, but on heating in a Clll'l'ent of chlorine a large amount of Si O2 (about 30 %) was left behind showing that even this process does not lead to pure amorphous silicon. Much more simple is the preparation of crystallised silicon accor­ ding to the method recently published by R. A. KÜHNE (Chem. Centr. 1904, r. 64) if we introduce a slight modification. A mixture of 200 grams of aluminium shavings or powder, 250 grams of sulphur and 180 gl'ams of fine sand is put into a Hessian crucible placed in a bucket with sand. Upon the mixture is sprinkled a thin layer of magnesium powder and this is ignited by means of a GOLDSCHMIDT cartrÛIge. The mass burns with a beautiful light and the contents of the crucible beeome white hot. When eold, the mass is treated with dilute hydrochloric acid, which dissolves the aluminium sulphide nnd leaves the silicon in a beautifully crystallised state. The yield amounts to about 30 gl'ams. On heating in a CUl'rent of chlorine Si C1 4 is very l'eadily formed, only 3% remaining as non­ volatile pl'oducts. It is a material eminently suited for the pl'epa­ ration of Si 01 4, but Mr. SLIJPER did not succeed in converting it into r,ilicon sulphide by heating with sulphur. G1'oningen, Lab. Univers. March 1904.

Crystallography. - "Un the p1'eservütion of the c1'ystallogmphical symmetry in the substitution of position isomeric derivatives of the benzene series". By Dr. F. M. JAEGER. (Oommunicated by Prof. A. P. N. FRANCHIMONT). (Communicated in the meeting of June 24, 1904).

Some time ago when engaged in a research as to the connection between molecular and crystallographical symmetry of position-isomeric 1 benzene derivatives ), I demonstrated, that of the six possible t1'ibromo-

1) JAEGER, Crystallographic and Molecular Symmetry of position·isomeric Benzene­ derivatives. Dissertation, Leiden 1903. (Duteh).

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